Video surveillance and monitoring systems are widely used to provide visual monitoring of locations and to thereby help detect intrusion, prevent loss or damage to property, provide public safety and the like. There is a general desire to make such surveillance and monitoring systems portable (e.g. for temporary and/or rapid deployment in a variety of environments). Examples of situations having a need for temporary and/or rapid deployment surveillance and monitoring system include emergency situations, such as riots, hostage takings, fires, chemical spills or the like, and special event situations, such as public gatherings, meetings of dignitaries or the like.
Current digital video surveillance and monitoring systems incorporate image capturing device(s) (i.e. camera(s)) which have hardwired connections to AC power and hardwired video transmission connections between the remotely located cameras and a central monitoring location. The hardwired connections to the central monitoring location permits captured video data to be received at the central monitoring location. Such systems are not transportable and are not suitable for applications where it is desired to temporarily and/or rapidly deploy one or more cameras in a variety of environments. There is a need for video surveillance and monitoring systems using wireless camera devices which may be rapidly and/or temporarily deployed to monitor a region of interest.
Digital wireless communication systems incorporating bi-directional point to multipoint digital communications typically incorporate one of two antenna types: omni-directional antennas; and high gain directional antennas. For a given transmission power (which is typically limited by FCC regulations), each of these two antenna types has its own advantages and limitations.
Omni-directional antennas transmit and receive electromagnetic energy in all azimuthal directions and, consequently, there is generally no need to point transmitting and receiving omni-directional antennas toward one another. Omni-directional antennas are generally suitable if the radio path is relatively short and/or the data rate is relatively low. Directional antennas transmit and receive electromagnetic energy preferentially in a particular direction. Examples of directional antennas include patch, panel and Yagi antennas. The ability of a directional antenna to preferentially transmit and receive radiation in a particular direction is referred to as antenna gain. Because of antenna gain, directional antennas are suitable for use over relatively long radio path lengths and/or for relatively high data rates.
Most radio communication systems experience interference from other radio frequency sources, such as other units within the system, foreign radio systems and unintentional radiators, for example. Also, most radio communication systems experience multipath effects. These multipath effects may be due to radio reflections from objects between or close to the communicating radio devices, resulting in signals arriving via different paths and having different time delays. Multipath propagation can result in delay spread, a type of distortion resulting in the spreading out or “smearing” of the received signal and a frequency response that has nulls, which are frequencies where the multiple receive signals add in a destructive manner to reduce the received signal strength. Systems using omni-directional antennas receive energy from all directions at once and therefore tend to experience relatively poor multipath performance when compared to systems using directional antennas.
In order to achieve the advantages of antenna gain (i.e. relatively long radio path length, relatively high data rate and relatively good multipath performance), a directional antenna on a receiving wireless unit must be pointed at the transmitting wireless unit and/or vice versa. The need for pointing directional antennas is inconvenient where it is desired to rapidly and/or temporarily deploy wireless camera devices for video surveillance of a region of interest. In addition, the people deploying such camera devices may not have knowledge of antenna theory or RF transmission and may not comprehend how to properly point a directional antenna.
There is a general desire to provide portable video surveillance and monitoring systems (e.g. for temporary deployment in a variety of environments) which address or ameliorate some of the issues discussed above.